Apparatus and method for minimizing solids deposited in a reserve pit

ABSTRACT

A method of minimizing the quantity of solids deposited in a reserve pit of the type used in drilling oil and gas wells. The method is applicable to well sites where drilling is facilitated by the use of drilling fluid and cuttings are generated by a drill bit, lifted to the surface and deposited at a well bore. The method consists of separating cuttings from associated drilling fluid and conveying larger cuttings to a solids storage location, thus bypassing the reserve pit for a good deal of the solid waste generated at a drilling site. Residual drilling fluid is directed to a reservoir such as a suction tank where it can be reused in further drilling operations. Over time the residual drilling fluid in the suction tank will increase in viscosity to the point where the residue is no longer suitable as drilling fluid. Thereupon, a portion of the residue may be discarded from the suction tank to the reserve pit and water or drilling chemicals added to the suction tank to revitalize the drilling fluid.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 60/411,263, “Apparatus and Method for Minimizing Solids Deposited in a Reserve Pit,” filed Sep. 17, 2002, incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Technical Field

[0003] The present invention is directed toward the handling of waste materials generated during the drilling of an oil or gas well, and more particularly toward a method of minimizing the quantity of solids deposited in a reserve pit of the type used in drilling oil or gas wells.

[0004] 2. Background Art

[0005] The exploration for oil and gas dates back over 100 years in the United States. The technology to drill wells faster and deeper is constantly being enhanced to reduce costs and improve profit margin for the oil companies. Exploring for these resources takes a tremendous amount of money and cooperation between the oil companies and the service industry employed to look for oil and gas.

[0006] While drilling a well, cuttings (earth) generated by the bit are brought back to the surface by a drilling fluid comprised of water, bentonite, and polymers and other assorted chemicals. The disposal of these cuttings has always been a significant well site issue. Historically, cuttings have been disposed of into a waste pit called a reserve pit. Recently, the practice of drilling more then one well from a single pad and environmental concerns have made the size and existence of a reserve pit a liability.

[0007] Presently, wastes generated at a well site are handled by the implementation of one or two mutually exclusive site management methods. The two methods are broadly categorized as open loop systems and closed loop systems. The most common and traditional mode is an open loop system. In a typical open loop system, a reserve pit is dug adjacent to the well site to hold excess cement from casing designs, rig water used to clean the rig, excess drilling fluids, and most importantly for the disposal of drill cuttings. A typical open loop system is quite cost effective, however, it requires a large reserve pit which raises significant environmental concerns. In many instances, the size of the reserve pit is dictated by the volume of drill cuttings dumped therein. The size of a reserve pit sufficient to handle multiple wells drilled from a single pad can be environmentally prohibitive.

[0008] The second, more costly alternative to an open loop system is to drill with a closed loop mud system eliminating the need for a reserve pit. The hallmark of all closed loop systems is the use of a rather complex apparatus and methodology to separate drilling fluid from drill cuttings and other waste matters associated with the drilling process. After separation, the cuttings and waste are removed from the drilling site in solid form, and the drilling fluid is reused. Numerous examples of closed loop systems are taught in the prior art. Each of these systems is more or less effective at facilitating the handling of waste generated at a drill site, yet each is relatively expensive. The increased cost arises from both additional equipment expenses and significantly increased manpower costs in order to monitor and operate the relatively sophisticated closed loop equipment. Examples of closed loop systems include Summers, U.S. Pat. No. 4,636,308, which teaches a series of rig shakers, rig de-sanders, rig de-silters, and centrifuges to effectively remove solids from the drilling fluid. It is an expressly stated purpose of the Summers invention to eliminate the reserve pit at a drilling site, thus reducing the area required and an environmental pollution problem.

[0009] Similarly, Rowney, et al., U.S. Pat. No. 6,059,977, teaches a closed loop system featuring a settling tank which decreases the reliance on a battery of centrifuges. McIntyre, U.S. Pat. No. 6,530,438, features a closed loop system using a desorption unit that vaporizes the liquids from the cuttings, then condenses the vapor for reuse as drilling fluid. Other closed loop systems are based upon flocculation tanks or other chemical methods to effectively separate undesirable solids from the drilling fluid.

[0010] Although the above closed loop technologies are effective and environmentally sound, each involves significant cost. In addition, the elimination of a reserve pit can cause site management problems. In particular, it is customary to wash solid contaminants off of the drilling rig and associated equipment into the reserve pit. For example, a cement truck which might need to be cleaned can simply be hosed off with the excess cement being washed into the reserve pit of an open loop system. On the other hand, there is no facility available for routine maintenance chores such as this in conjunction with a closed loop system.

[0011] The present invention is directed to overcoming one or more of the problems discussed above.

SUMMARY OF THE INVENTION

[0012] In one aspect of the present invention, a method of minimizing the quantity of solids deposited in a reserve pit of the type used in drilling oil and gas wells is disclosed. The method is applicable to well sites where drilling is facilitated by the use of drilling fluid and cuttings are generated by a drill bit, lifted to the surface and deposited at a well bore. The method consists of the following steps:

[0013] 1. Directing the cuttings and associated drilling fluid from the well bore to a coarse separating means such as a rig shaker;

[0014] 2. Separating larger cuttings from a residue consisting of drilling fluid and associated smaller cuttings by action of the rig shaker;

[0015] 3. Conveying the larger cuttings from the rig shaker to a solid storage location, thus bypassing the reserve pit for a great deal of the solid waste generated at the drilling site;

[0016] 4. Directing the residue from the rig shaker to a reservoir such as a suction tank where it can be reused as drilling fluid in further operations;

[0017] Implementation of the above steps will, over time, cause the residue in the suction tank to increase in viscosity to the point where the residue is no longer suitable as drilling fluid.

[0018] 5. Discarding a portion of the residue from the suction tank to the reserve pit.

[0019] Water or drilling chemicals may then be added to the suction tank to revitalize the drilling fluid.

[0020] The large cuttings may alternatively be directed from the rig shaker to a drying apparatus prior to depositing the larger cuttings at the solids storage location. If the size of the reserve pit is to be minimized and the useful lifespan of the reserve pit maximized, hydrocyclones and/or centrifuges may be used in series with the rig shaker to remove relatively finer materials from the residue prior to return of the residue to the suction tank for reuse as drilling fluid. Implementation of the above method assures that a reserve pit will be available at the drilling site for ancillary uses such as cleaning equipment.

[0021] An alternative embodiment of the present invention is an apparatus for handling the cuttings associated with the drilling of an oil or gas well. The apparatus is suitable for implementation of the above method and has the following components: a device for the coarse separation of cuttings from a residue of fine cuttings and drilling fluid, such as a rig shaker; a solids storage location receiving the cuttings from the rig shaker; a suction tank receiving residue from the rig shaker; a plumbed loop for returning the residue from the suction tank to the well for use as drilling fluid in further operations; and a reserve pit for receiving a discarded portion of the residue from the suction tank when the viscosity of the discarded portion renders it no longer suitable as drilling fluid.

[0022] The apparatus may alternatively have devices for separating medium and fine particles from the residue such as hydrocyclones or centrifuges of various sizes in series with the rig shaker. Implementation of these supplemental devices in the apparatus can further minimize the amount of solids ultimately deposited into the reserve pit. Preferably, the larger cuttings are conveyed from the rig shaker by a mechanical device such as a conveyor belt or auger.

[0023] A system designed and implemented as described above will not be as costly as a closed loop mud system without a pit. By removing the drill cuttings with the solids control equipment and avoiding disposal into the reserve pit, a much smaller pit is needed. By keeping the solids out of a standard reserve pit, the basic pit can be reduced in size by 66% for a given operation. Some of the advantages to a smaller pit are the following:

[0024] 1. Less water needed;

[0025] 2. Construction costs of the pit will be less;

[0026] 3. Reduction of the expense incurred for reclaiming the larger pit;

[0027] 4. Significantly decreased operating costs compared to a closed loop pitless system;

[0028] 5. Small pit available to recycle waste fluids such as rig wash down water and FRAC flow back;

[0029] 6. The smaller pit will minimize environmental surface damage.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a schematic representation of an apparatus for minimizing solids deposited in a reserve pit;

[0031]FIG. 2 is a flow chart representation of the method of the present invention; and

[0032]FIG. 3 is a flow chart of the method of the present invention featuring hydrocyclones and centrifuges in series to remove relatively finer solids.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0033] An apparatus for minimizing the deposit of solids in a reserve pit 10 is illustrated schematically in FIG. 1. The apparatus receives combined drilling fluid and drill cuttings from a well bore 12 through a flowline 13. The combined cuttings and drilling fluid are directed to a rig shaker 14 which separates larger cuttings (e.g. 100 micron or bigger) from the drilling fluid. The drilling fluid may then be directed through a flowline tank 15 to a suction tank 16. Alternatively, the drilling fluid recovered from the rig shaker 14 may be directed by line 18 to a hydro cyclone 20 for removal of smaller sized particulate matter (e.g. 50-100 micron or bigger). The separated drilling fluids may then be directed through the flowline tank 15 to the suction tank 16, and from there through line 17 to the well bore 12 for reuse as drilling fluid. Alternatively, the drilling fluid separated by the rig shaker 14 and the hydro cyclone 20 may be directed by line 24 to a centrifuge 26 for separating even smaller particulate (e.g. 50 micron or smaller) material from the drilling fluids. Drilling fluid recovered from the centrifuge is then returned by line 28 to the suction tank 16. As should be apparent to one skilled in the art, whether the hydro cyclone 20 or centrifuge 26 are used in combination with the rig shaker for further removal of solids is a function of the need to remove particulate material of a size smaller than that separated by the rig shaker 14 from drilling fluid being returned to the suction tank 16. Either the hydro cyclone 20 or the centrifuge 26 may be omitted from the apparatus when removal of particulate material of the size removed by these devices is unnecessary.

[0034] As shown in FIG. 1, solids separated from the rig shaker 14 are collected by solids transport device 30 which may be a conveyer belt or, preferably, an auger. The solids transport device 30 may also receive solids separated from the hydro cyclone 20 when the hydro cyclone 20 is part of the apparatus 10. The solids are transported from the rig shaker 14 and hydro cyclone 20 to a solids dryer 32 to remove residual drilling fluids from the solids and the solids are preferably outputted to a three sided tank 34. The three sided tank 34 facilitates removal of the separated solids by a front end loader or the like for transport from the vicinity of the well bore or for deposit near the well bore. Alternatively, the solids dryer 32 may be omitted and the wet solids captured at the solids transport device outlet may then be air dried either in the vicinity of the well bore or elsewhere. Where a centrifuge 26 is used, solids extracted by the centrifuge are deposited in a three sided tank 36 for disposal in the same manner as the solids deposited in the three sided tank 34.

[0035] As described above, the suction tank 16 receives a residue of drilling fluid and fine cuttings through the flowline tank 15 from the rig shaker 14, hydrocyclone 20 and centrifuge 26 (if the hydrocyclone 20 and centrifuge 26 are implemented). Over time, as the residue is pumped through line 17 to the well bore 12 for reuse as drilling fluid, the viscosity of the residue in the suction tank 16 will increase to a point where the residue is no longer suitable for use as drilling fluid. As shown in FIG. 1, a discard portion of the thickened residue can then be directed to the reserve pit 38 through discard line 40. The drilling fluid/residue mixture in the suction tank 16 can be recharged with additional drilling fluid or water after the discarded portion of the residue has been removed.

[0036] The rig shaker 14, hydrocyclone 20, solids transport device 30, solids dryer 32 and centrifuge 26 may be selected from various known manufactures and may be off the shelf units. A representative rig shaker model is the Flo-Line Cleaner, manufactured by Derrick. Representative hydro cyclones are models 4″-10″ cones, manufactured by Derrick. A representative auger is the Screw Conveyor model, manufactured by Martin. A representative solids dryer is the High G Dryer, manufactured by Derrick. A representative centrifuge is model DE-1000, manufactured by Derrick.

[0037] In an alternative configuration, the solids transport device 30 may be omitted if the solids from the rig shaker 14 and hydro cyclone 20 fall directly into the solids dryer 32. However, there must be enough room behind the flowline tank 15 and the reserve pit 38. This may require an unconventional routing trench system to allow access to the reserve pit 38. However, in most applications, use of a solids transport device 30 to remove the solids from the drilling platform is preferred.

[0038] The apparatus described above can be used to implement a method of managing the cuttings generated at an oil or gas well drill site. The method is represented by the flowchart of FIG. 2. The method commences with cuttings and drilling fluid being forced to the surface of a drill bore as drilling operations progress (step 100). The combined cuttings and drilling fluid are routed to a device for separating coarse cuttings from a residue of drilling fluid and finer cuttings (step 110). A typical device for separating coarse cuttings from the residue is a rig shaker 14. Following step 110, the large cuttings are conveyed to a solid storage location (step 112) contemporaneously the residue of drilling fluid and finer cuttings are routed to a reservoir such as a suction tank 16 (step 114). Typically, the drilling fluid and finer cuttings flow through a flowline tank 15 situated in close proximity to the suction tank 16. The residue of drilling fluid and finer cuttings is recycled to the well bore 12 for use as drilling fluid in further drilling operations (step 116). As a result of this continual cycle of reuse and with the continuous addition to the residue of fine cuttings, over time the residue in the suction tank 16 will thicken to an unusable viscosity (step 118). At the point in time where the viscosity of the residue renders it no longer suitable for use as drilling fluid, the operator can direct a discard portion of the residue in the suction tank to the reserve pit (step 120). This step will substantially or partially drain the suction tank 16 which can be recharged with fresh drilling fluid or water.

[0039] In addition to the basic method of FIG. 2, certain enhancements to the process are represented in flowchart form on FIG. 3. In particular, the residue of smaller cuttings and drilling fluid from the rig shaker 14 may be directed to an apparatus for removing smaller cuttings such as a hydrocyclone (step 122). If it is desired to remove even finer materials from the residue, the fine cuttings and associated drilling fluid can be directed to a centrifuge 26 (step 124) before the residue flows to the suction tank 16. As described above, the larger cuttings from the rig shaker 14 and the smaller cuttings from the hydrocyclone 20 may be placed at an appropriate location for air drying. Alternatively, these solids can be delivered to an apparatus for drying solids, such as a high-g solids dryer 32 (step 126). Subsequently, the dried solids may be routed to a 3-sided tank 34 for temporary storage (step 128) prior to delivery to a final solids storage location (step 112).

[0040] The reserve pit 38 of the invention can be substantially smaller than the reserve pit associated with a conventional open loop drilling system. This decrease in size is facilitated by the removal and processing of the solid cuttings which traditionally are dumped into the reserve pit 38. The availability of the small reserve pit 38 has advantages as water from well site wash down, associated equipment wash down and frac flow back can be directed to the reserve pit 38 for safe and efficient storage (step 130).

[0041] The objects of the invention have been fully realized through the embodiments disclosed herein. Those skilled in the art will appreciate that the various aspects of the invention may be achieved through different embodiments without departing from the essential function of the invention. The particular embodiments are illustrative and not meant to limit the scope of the invention as set forth in the following claims. 

What is claimed is:
 1. A method of minimizing the quantity of solids deposited in a reserve pit of the type used in drilling oil or gas wells where drilling is facilitated by the use of drilling fluid and cuttings are generated by a drill bit, lifted to the surface and deposited at a well bore, the method comprising the steps of: a. directing the cuttings and associated drilling fluid from the well bore to a coarse separating means; b. separating larger cuttings from a residue comprising drilling fluid and associated smaller cuttings by action of the coarse separating means; c. conveying the larger cuttings from the coarse separating means to a solids storage location; d. directing the residue from the coarse separating means to a reservoir; e. returning the residue from the reservoir to the well for use as drilling fluid in further drilling operations; and f. discarding a portion of the residue from the reservoir to the reserve pit when the viscosity of the discarded portion renders it no longer suitable as drilling fluid.
 2. The method of claim 1 wherein the coarse separating means is a rig shaker.
 3. The method of claim 1 wherein the larger cuttings are conveyed from the coarse separating means an auger.
 4. The method of claim 1 wherein the coarse separating means separates cuttings too large to fit through a 100 micron screen from the residue.
 5. The method of claim 1 wherein step c. comprises: conveying the larger cuttings from the coarse separating means to a means for drying solids; drying the larger cuttings in the means for drying solids creating dried solids; and conveying the dried solids to the solids storage location.
 6. The method of claim 7 wherein the means for drying solids is a High-G dryer.
 7. The method of claim 1 wherein step d. comprises: directing the residue from the coarse separating means to a medium separating means; separating smaller cuttings from the residue by action of the medium separating means; directing the residue from the medium separating means to the reservoir; and conveying the smaller cuttings from the medium separating means to the solids storage location.
 8. The method of claim 7 wherein the medium separating means is a hydrocyclone.
 9. The method of claim 7 wherein the medium separating means separates cuttings too large to fit through a 50 micron screen from the residue.
 10. The method of claim 7 wherein the residue is further conveyed to a fine separating means prior to the reservoir, the method further comprising: separating fine cuttings from the residue by action of the fine separating means; directing the residue from the fine separating means to the reservoir; and conveying the fine cuttings from the fine separating means to the solids storage location.
 11. The method of claim 10 wherein the fine separating means is a centrifuge.
 12. An apparatus for handling the cuttings associated with the drilling of an oil or gas well where drilling is facilitated by the use of drilling fluid and cuttings are generated by a drill bit, lifted to the surface and deposited at a well bore, the apparatus comprising: coarse separating means receiving the cuttings and associated drilling fluid from the well bore and separating the larger cuttings from a residue comprising smaller cuttings and drilling fluid; a solids storage location receiving the larger cuttings from the coarse separating means; a reservoir receiving the residue from the coarse separating means; means for returning the residue from the reservoir to the well for use as drilling fluid in further drilling operations; and a reserve pit receiving a discarded portion of the residue from the reservoir when the viscosity of the discarded portion renders it no longer suitable as drilling fluid.
 13. The apparatus of claim 12 wherein the coarse separating means is a rig shaker.
 14. The apparatus of claim 12 wherein the means for conveying the larger cuttings from the coarse separating means is an auger.
 15. The apparatus of claim 12 further comprising a solids dryer receiving the larger cuttings from the separating means.
 16. The apparatus of claim 12 further comprising a medium separating means receiving the residue from the coarse separating means.
 17. The apparatus of claim 16 wherein the medium separating means is a hydrocyclone.
 18. The apparatus of claim 16 further comprising a fine separating means receiving the residue from the medium separating means.
 19. The apparatus of claim 18 wherein the fine separating means is a centrifuge.
 20. An apparatus for handling the cuttings associated with the drilling of an oil or gas well where drilling is facilitated by the use of drilling fluid and cuttings are generated by a drill bit, lifted to the surface and deposited at a well bore, the apparatus comprising: a rig shaker receiving the cuttings and associated drilling fluid from the well bore and separating the larger cuttings from a residue comprising smaller cuttings and drilling fluid; an auger conveying the larger cuttings from the rig shaker to one of a solids dryer and a three sided tank; a reservoir receiving the residue from the rig shaker; a return loop in fluid communication with the reservoir and the well bore for returning the residue in the reservoir to the well for further drilling operations; and a reserve pit receiving a discarded portion of the residue from the reservoir when the viscosity of the discarded portion renders it no longer suitable as drilling fluid. 